Interpretive Summary: Classical swine fever virus (CSFV) has three glycoproteins (proteins with a high content of sugars in their molecules) in its external membrane (E(rns), E1 and E2). Here we analyzed the effects of lack of sugar in the immunogenicity of E(rns), E1, and E2 proteins. All three proteins lacking glycosylation, failed to induce a detectable virus neutralizing antibody response and protection against CSFV. In addition, it was observed that single administration of purified E(rns) glycoprotein induced an effective protection against CSFV infection.

Technical Abstract:
Classical swine fever virus (CSFV) harbors three envelope glycoproteins (E(rns), E1 and E2). Previous studies have demonstrated that removal of specific glycosylation sites within these proteins yielded attenuated and immunogenic CSFV mutants. Here we analyzed the effects of lack of glycosylation of baculovirus-expressed E(rns), E1, and E2 proteins on immunogenicity. Interestingly, E(rns), E1, and E2 proteins lacking proper post-translational modifications, most noticeable lack of glycosylation, failed to induce a detectable virus neutralizing antibody (NA) response and protection against CSFV. Similarly, no NA or protection was observed in pigs immunized with E1 glycoprotein. Analysis of E(rns) and E2 proteins with single site glycosylation mutations revealed that detectable antibody responses, but not protection against lethal CSFV challenge is affected by removal of specific glycosylation sites. In addition, it was observed that single administration of purified E(rns) glycoprotein induced an effective protection against CSFV infection.